Coates, the Harvard-educated pastor of Mt. Ennon Baptist Church in Clinton, was growing uncomfortable with how colleagues were talking about homosexuality when same-sex marriage become a hot topic in 2011 because of legislative debate on the issue.
"Listening to the tone and the rhetoric they were using, that rhetoric did not reflect my views," he said. "I did not want my silence to be interpreted by anyone as an endorsement of that position."
He also had a personal connection to the question. Growing up, Coates enjoyed a close bond with a relative who suddenly stopped coming to family events when they both went off to college.
"He disappeared," Coates said.
He eventually learned that the relative was gay and HIV-positive. Nobody in the family wanted to talk about it.
"I wrestled with that code of silence that many families have when somebody is different," he said. "I didn't want the church to be that way."
Hickman, of Southern Baptist Church in East Baltimore, also started thinking about same-sex marriage in 2011, after O'Malley said he would make legalization a priority.
"People were saying pastors will be locked up for resisting a same-sex ceremony," he recalled. "I said we should get a better understanding of what it was."
Hickman and Coates — longtime friends — conferred and decided they wanted to be part of the debate in some way.
Hickman, who knew O'Malley from his years as mayor of Baltimore, called the governor's office.
The response: Come to Annapolis. The governor wants to have lunch with you.
From there, Hickman and Coates began inching toward what would eventually be a historic campaign. They discussed religious freedom with O'Malley. They liked the way he talked about it.
O'Malley invited the men back to the governor's mansion the next day, for the breakfast and launch of the legislative battle.
A gay-rights activist approached Hickman and thanked him for his support.
"I said, 'I don't support same-sex marriage. I support your right to get married in a courthouse,'" Hickman recalled.
He says the man understood the distinction he was drawing, and that helped Hickman get closer.
The governor's office asked whether Hickman and Coates would testify at a House of Delegates hearing on the bill. They chewed over the implications together. How would the church respond? The broader faith community? Was this a step too far?
In the end they agreed. Hickman, seated at a table with O'Malley and Coates, explained his thinking to lawmakers: "Let the church be the church, the state be the state and God be the judge."
The General Assembly approved the legislation and O'Malley signed it in March.
Opponents responded by petitioning the measure to referendum. The law was suspended and put on the ballot, where voters would have the final say.